Social badge support for static previews (#2871)

The static previews don't support the social badges. Adding that lets us remove support for `exampleUrl`. Close #2479.

This includes `style` and `namedLogo` in the service-definition export and updates the frontend to use it. To accomplish this, it passes `namedLogo` through `coalesceBadge`. After logo resolution is moved to `makeBadge` this duplication can be removed, as `logo` will no longer be needed in the result of `coalesceBadge`.

services/github/github-followers.service.js

@@ -30,22 +30,26 @@ module.exports = class GithubFollowers extends LegacyService {
     return [
       {
         title: 'GitHub followers',
-        previewUrl: 'espadrine',
-        // https://github.com/badges/shields/issues/2479
-        // namedParams: {
-        //   user: 'espadrine',
-        // },
-        // staticPreview: {
-        //   label: 'Follow',
-        //   message: '150',
-        //   style: 'social',
-        // },
-        queryParams: { style: 'social', label: 'Follow' },
+        namedParams: {
+          user: 'espadrine',
+        },
+        staticPreview: {
+          label: 'Follow',
+          message: '150',
+          style: 'social',
+        },
+        queryParams: { label: 'Follow' },
         documentation,
       },
     ]
   }
 
+  static get defaultBadgeData() {
+    return {
+      namedLogo: 'github',
+    }
+  }
+
   static registerLegacyRouteHandler({ camp, cache, githubApiProvider }) {
     camp.route(
       /^\/github\/followers\/([^/]+)\.(svg|png|gif|jpg|json)$/,